Abstract: The tensile experiment of TC4 high lock bolts assembled in clamps with different angle was carried out to obtain the tensile strength and it revealed the effect of assembly angle on tensile strength of the bolts. Combined with the fracture analysis, the underlying mechanism was discussed. The results show that the tensile strength of high lock bolt decreases to 70% of original bolt when the assembly angle increases from 0° to 5°. The reason is attributed to the turn of the original tensile load into a complex load by change of assembly angle, the fracture location changes from the second thread to the bolt head. The results can contribute to understanding the effect of assembly angle on the load carrying capacity of high-lock bolts and provide a strategy to design its assembly specification.